Patent GB-627822-A (GB)
Title: Improvements in electrical driving mechanism
IPC: B66C13/26
Filed: 1947-09-30
Abstract: 627,822. Transmitting mechanical power. HEENAN & FROUD, Ltd., and HAYES, C. T. Sept. 30, 1947, No. 20533. [Class 38 (iv)] A hoisting drum 17 of a crane or the like is operated at variable speed and torque from a constant speed A.C. motor 1 through an eddycurrent coupling 5, the field 13 of which is supplied with D.C. from an electronic excitation unit comprising grid-controlled rectifiers 65, 67 associated with a manual controller 43, 45, whereby the voltage output of the unit is regulated. An electromagnetically released friction brake 21, 27 acting on the driven member of the coupling is also operated by the controller. The coupling may drive the drum 17 through gearing 19 and a positive reverse drive for lowering an unloaded hook may be provided by gearing 34 driven by a second eddy-current coupling 35 energized from a transformer 59 and rectifier bridge 229 over contacts 237 which are closed when the controller handle 45 is moved. past a predetermined position in the " lowering " direction. The control voltage for, the grid of the leading rectifier 67 comprises the following components : (1) an A.C. component derived from one phase of the main power supply through transformer 79 and phase-shift circuit 81, 82 ; (2) a variable D.C. component of magnitude determined by the position of the controller arm 45 and obtained from the mains supply over transformer 55, rectifier 117 and voltage stabilizer tube 121 ; (3) an opposing D.C. component proportional to the speed of the hoisting drum 17 and derived from transformer-rectifier unit 91. or 93 which is energized by a tachometer alternator 29 driven by the output member of the coupling 5; and (4) a D.C. component proportional to the motor current and developed across a resistor 159 associated with the stabilized source and carrying the current of a valve 147, the conductivity of which is controlled by a current transformer 141 in the motor feed line. Component (3) stabilizes the load speed at that selected by the controller, whilst component (4) prevents overloading of the motor. Movement of the controller arm 45 from the neutral position (to which it is spring biassed and in which position associated cam-operated switches 47, 195 prevent energization of contactor coils 300, 200 controlling brake-release and coupling excitation) to the "raise" (left-hand) section of the controller potentiometer 43 closes switches 47, 195 to release the brake and apply coupling excitation-subject to closure of both of (1) a switch 199 which may be actuated separately from, or in conjunction with, the controller arm, and (2) the contacts 177 of and under-voltage relay 165. The controller arm movement also opens a cam switch 48 to de-energize a relay coil 100, whereby its change-over contacts 100A, 102, 100C; 100D assume the positions shown and establish the correct series of voltage-component sources for grid control of the rectifier 67 during " raising." Movement of the controller arm to the opposite side of the neutral position causes closure of the cam switch 48, thereby energizing relay 100 which changes over to establish the series of voltage-component sources necessary during " lowering." Closure of a switch 201, instead of switch 199, is necessary before the brake can be released and the coupling energized in this position of the controller arm. During " lowering " the coupling acts as an eddy-current brake on the load, the control-voltage components for rectifier 67 acting to maintain the load speed at that set by the controller arm. Specifications 576,620 and 578,368 are referred to.